We previously purified a soluble phosphatidic acid-preferring phospholipase A1 from bovine testis and cloned and sequenced its cDNA. This enzyme could potentially play an important role in phosphatidic acid-dependent cell signaling, but this role remains to be defined. Studies of the distribution of the enzyme's mRNA in human tissues demonstrated several reactive components, which were distributed differently in the testis, brain, and other tissues. Studies with antibodies to the bovine enzyme demonstrated cross-reactive material in macaque tissues including the testis. The testis enzyme could be precipitated from the high-speed supernatant of macaque testis homogenates with antibodies to the protein kinase, CK2. Furthermore, a recombinant form of the alpha subunit of CK2 could catalyze the phosphorylation of both native and recombinant forms of the phospholipase A1; and recombinant forms of the alpha subunit of CK2 and the phospholipase could form a tightly associa ted comple x. These results raise the novel possibility that CK2 may in some way regulate the function of the phospholipase, and attempts to test this possibility are currently underway. In addition, in situ hybridization and immunocytochemical studies are planned to examine the possibility that the mRNAs and proteins that correspond to CK2 and the phospholipase may be coexpressed. Another finding of potential interest is that material that cross-reacts with antibodies to the phospholipase is present in spermatozoa from the cauda epididymis. This material is of relatively low molecular mass (approximately 30 KDa) and is tightly associated with the tail. We are currently attempting to isolate amounts of this material sufficient for sequence analysis by mass spectroscopy. FUNDING NIH grant RR00166 and the Howard Hughes Medical Institute. Hollenback, D. and Glomset, J.A. On the relation between a stearoyl-specific transacylase from bovine testis membranes and a co-purifying acyltransferase. Biochemistry 37 363-376, 1998. Higgs, H.N., Han, M.H., Johnson, G.E., and Glomset, J.A. Cloning of a phosphatidic acid-preferring phospholipase A1 from bovine testis. J. Biol. Chem. 273:5468-5477, 1998. [This project was also reported in the Neuroscience Core section.]